Method and apparatus for distinguishing cells with the same physical cell identifier

ABSTRACT

A method ( 700, 800 ) and apparatus ( 500, 600 ) for distinguishing cells with the same physical cell identifier is disclosed. The method can include receiving ( 820 ) a handover request message including target cell timing offset information at a potential target cell base station, where the potential target cell base station can have a physical cell identifier. The method can include comparing ( 830 ) the received target cell timing offset information with stored timing offset information at the potential target cell base station. The method can include sending ( 840 ) a handover request accept message if the received target cell timing offset information is substantially equal to the stored timing offset information. The method can also include receiving ( 720 ), at a wireless terminal, a target cell physical cell identifier and determining ( 730 ) a target cell timing offset of a radio frame of the target cell with respect to reference timing of a serving cell. The method can include sending ( 740 ) a measurement report including the target cell physical cell identifier and the target cell timing offset.

BACKGROUND

1. Field

The present disclosure is directed to a method and apparatus fordistinguishing cells with the same physical cell identifier. Moreparticularly, the present disclosure is directed to distinguishing cellswith the same physical cell identifier by using a radio frame timingoffset.

2. Introduction

Presently, in a cellular network, cells use physical cell identifiers todistinguish themselves from each other. An operator ensures that aphysical cell identifier unambiguously identifies a base station.However, Closed Subscriber Group (CSG) base stations, such as accesspoints, may use the same physical cell identifiers, which can result inphysical cell identifier confusion. For example, CSG cells can be acollection of cells used for deployment in a campus or can be individualcells used for deployment in users' homes. The CSG cells co-exist withmacro cells on the same carrier frequency. CSG cells have a smallercoverage area than macro cells. Unlike macro cells, the CSG cells areun-planned, in that the operator has much less control over theirplacement and configuration than with macro cells. Thus, two CSG cellsthat are located within the coverage of the same macro cell can use thesame physical cell identifiers. Unfortunately, this results in physicalcell identifier confusion.

To elaborate, a mobile station uses physical cell identifiers (PCID)during synchronization and during cell ranking. The mobile station rankscells by measuring the received signal strength and then uses theranking to facilitate handover and reselection. If a PCID is notguaranteed to be unique within a macro cell, then PCIDs cannot be usedfor reselection and handover. If PCIDs cannot be used for reselectionand handover, a mobile terminal would need to read system information ofthe target cell and acquire the cell global identity to determine if itis allowed to access the cell. Unfortunately, this requires considerableadditional battery usage in idle mode and can seriously impact batterylife. Another problem with using the same PCIDs is that mobile stationcell handover will fail when there is more than one cell with the samePCID and a network cannot determine which cell is the right one forhandover.

A range of PCIDs can be reserved for CSG cells. Also, a mobile terminalcan have a list of CSG PCIDs, such as a CSG white-list of cells that itis allowed to access. These restrictions limit the problem in thereselection case to when the target cell is a CSG cell in the CSGwhite-list. However, PCID confusion can still frequently occur inmetropolitan areas where more CSG cells are deployed. Even in caseswhere the spatial likelihood of PCID confusion is low, when confusionoccurs, it affects the same mobile terminal repeatedly. For example, iftwo homes within the coverage of the same macro cell use CSG cells withthe same PCID, the corresponding users will experience handover failureswhen entering their homes and they will have substantially higherbattery drain.

In order to resolve the PCID confusion, a mobile terminal could readadditional system information of a cell, which contains a unique cellidentifier, which the mobile terminal could rely on to determine if thecell is suitable. Unfortunately, reading the additional systeminformation in connected mode would cause substantial delay whichnegatively impacts handover performance. Also, a mobile terminal wouldhave to read the additional system information every time it encountersa CSG PCID, because different encounters with the same PCID couldcorrespond to different cells. Furthermore, the mobile terminal wouldlose data being sent through the serving cell as a result of reading theadditional system information because the mobile terminal would have tosynchronize to the target cell.

It is also possible to ignore a cell based on the PCID if it has beenfound to be unsuitable after previously reading additional systeminformation. However, this would not resolve the PCID confusion problembecause a cell encountered later may be suitable to the mobile terminalbut would be ignored if it has same PCID as a previously unsuitablecell. Furthermore, in connected mode, a mobile terminal would notmeasure and report the ignored PCIDs and the network would not know wheninterference from the PCID is significant and would not be able to takemeasures to prevent disruption of service.

Thus, there is a need for a method and apparatus for distinguishingcells with the same physical cell identifier.

SUMMARY

A method and apparatus for distinguishing cells with the same physicalcell identifier is disclosed. The method can include receiving ahandover request message including target cell timing offset informationat a potential target cell base station, where the potential target cellbase station can have a physical cell identifier. The method can includecomparing the received target cell timing offset information with storedtiming offset information at the potential target cell base station. Themethod can include sending a handover request accept message if thereceived target cell timing offset information is substantially equal tothe stored timing offset information. The method can also includereceiving, at a wireless terminal, a target cell physical cellidentifier and determining a target cell timing offset of a radio frameof the target cell with respect to reference timing of a serving cell.The method can include sending a measurement report including the targetcell physical cell identifier and the target cell timing offset.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which advantages and features of thedisclosure can be obtained, a more particular description of thedisclosure briefly described above will be rendered by reference tospecific embodiments thereof which are illustrated in the appendeddrawings. Understanding that these drawings depict only typicalembodiments of the disclosure and are not therefore to be considered tobe limiting of its scope, the disclosure will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is an exemplary block diagram of a system according to a possibleembodiment;

FIG. 2 is an exemplary timing offset illustration according to apossible embodiment;

FIG. 3 is an exemplary signal flow diagram according to a possibleembodiment;

FIG. 4 is an exemplary signal flow diagram according to a possibleembodiment;

FIG. 5 is an exemplary block diagram of a wireless communication deviceaccording to a possible embodiment;

FIG. 6 is an exemplary block diagram of a base station according to apossible embodiment;

FIG. 7 is an exemplary flowchart illustrating the operation of aterminal according to a possible embodiment;

FIG. 8 is an exemplary flowchart illustrating the operation of a basestation according to a possible embodiment;

FIG. 9 is an exemplary flowchart illustrating the operation of a basestation according to a possible embodiment; and

FIG. 10 is an exemplary flowchart illustrating the operation of a basestation according to a possible embodiment.

DETAILED DESCRIPTION

FIG. 1 is an exemplary block diagram of a system 100 according to apossible embodiment. The system 100 can include a terminal 110, aserving or macro cell 130 including a base station 135, a first targetor home cell 140, and a second target or home cell 150. The terminal 110may be a wireless communication device, such as a wireless telephone, acellular telephone, a personal digital assistant, a pager, a personalcomputer, a selective call receiver, or any other device that is capableof sending and receiving communication signals on a network includingwireless network. The first target cell 140 and the second target cell150 can be closed subscriber group (CSG) cells and can include their ownrespective base stations or access points 145 and 155. The first targetcell 140 and the second target cell 150 can have the same physical cellidentifier (PCID). The first target cell 140 and the second target cell150 can be located within a coverage area of the serving cell 130. Also,the coverage area of the first target cell 140 may or may not overlapthe coverage area of the second target cell 150.

The system 100 can be a wireless telecommunications network, such as aTime Division Multiple Access (TDMA) network, like a 3^(rd) GenerationPartnership Project (3GPP) Long Term Evolution (LTE) network, can be aUniversal Mobile Telecommunications System (UMTS), and/or can be otherlike communications systems. Furthermore, the system 100 may includemore than one network and may include a plurality of different types ofnetworks.

One or both of the base stations 145 and 155 can be a potential targetcell base station, such as a home base station, like a user basestation, a home NodeB, a Third Generation Partnership Project (3GPP)home NodeB and/or can be a closed subscriber group (CSG) base station,as defined in a third generation partnership project based standard orcan be any other home base station. A third generation partnershipproject home NodeB can also be a long term evolution (LTE) closedsubscriber group base station based on present third generationpartnership project long term evolution closed subscriber group basestation features. A long term evolution closed subscriber group basestation can include any base station that is a present or future resultof present and/or future modified third generation partnership projectlong term evolution closed subscriber group base station features. Ahome base station can also be a Universal Mobile TelecommunicationsSystem (UMTS) home base station.

In operation, the timing of the radio frames can be used to distinguishbetween cells even when they have the same physical cell identifier. Arange of physical cell identifiers can be reserved for closed subscribergroup cells, such as the target cells 140 and 150, and the terminal 110can be aware of the range of physical cell identifiers. The terminal 110can also have a closed subscriber group white list that includes a listof closed subscriber group cell physical cell identifiers that thatterminal 110 has access to.

If the terminal 110 is in idle mode, the terminal 110 can search for andrank cells based on received signal strength criteria. If a physicalcell identifier, P, such as a physical cell identifier of the targetcell 140, that is in the closed subscriber white-list is found, then theterminal 110 can store the timing offset, T, of the radio frame of thecell with respect to radio frames of the serving cell 130. The terminal110 can then read system information to determine if it is allowed toaccess the target cell 140. The terminal 110 can use the pair (P, T) toidentify the target cell 140. If the terminal 110 finds another cellwith the same physical cell identifier, P, it can compare timing offsetsto determine whether it has already found the cell.

Furthermore, if a cell corresponding to, for example, (P, T₁), is foundto be not suitable, (P, T₁) can be stored in the terminal 110. If theterminal 110 again encounters the physical cell identifier P, it candetermine the corresponding timing offset T₂. If T₁=T₂ within a certainaccuracy, the terminal 110 can conclude that the newly encounteredphysical cell identifier P corresponds to previously seen cell, and canignore the cell and not reselect to the cell regardless of the cell'sranking. If T₁≠T₂, within a certain accuracy, the terminal 110 canconclude that the newly encountered physical cell identifier does notcorrespond to the previously seen cell and may reselect to the new cell.When the serving cell changes and cell reselection occurs, the terminal110 can erase all stored (P, T) pairs.

In connected mode, the terminal 110 can measure candidate cells forhandover. If a terminal 110 finds and measures a candidate target cell,such as the cell 140, it can send a measurement report to the servingcell 130. The measurement report can include the radio frame time offsetof the cell 140 with respect to the serving cell 130. The source basestation 135 at the serving cell 130 can prepare all potential targetbase stations, such as base stations 145 and 155, that have the reportedphysical cell identifier by sending them a handover request thatincludes the radio frame time offset reported by the terminal 110. Thetarget cells 140 and 150 can then check the radio frame time offset andone can accept the handover request if the time offset is substantiallyequal to its radio frame time offset with respect to the terminal'sserving cell 130. If the handover request is accepted, the source basestation 135 can send a handover command to the terminal 110 instructingthe terminal 110 to hand over to the target cell 140 that both has thephysical cell identifier and transmits radio frames at the time offset.

In order to determine its own radio frame time offset relative to theserving or macro cell 130, a target or home cell 140 can have thecapability to receive a downlink signal from the macro cell 130.Alternatively, the radio frame time offset can be programmed into thehome cell 140 so that it always uses the same offset relative to themacro cell 130. Also, a home cell 140 can store its radio frame timeoffset with respect to more than one cell, which can be useful in caseswhere a home cell is placed at the edge of coverage of a cell and alsoin cases when there are no macro cells and handovers occur between homecells, such as cells 140 and 150.

If a home cell 140 does not have a downlink receiver, a terminal 110connected to the home cell 140 can be used to obtain radio frame timeoffsets relative to macro cells. For example, the terminal 110 canmeasure macro cell 130 timing information and report it to the home cell140, which can store the radio frame timing offsets with respect to eachrelevant macro cell.

If a home cell 140 does not have a downlink receiver and/or it does nothave any terminals connected to it, it may not know its own radio frametiming offset. In this case, an additional cell identifier, such as aclosed subscriber group identifier or a global cell identifier, of thehome cell 140 can be used to correctly identify it. To do this, aterminal 110 can send a measurement report, which can include the radioframe time offset of the home cell 140 with respect to the serving cell130. The source base station 135 can send a handover request to all thepotential target home base stations 140 and 150 that have the reportedphysical cell identifier by sending a handover request that includes theradio frame time offset reported by the terminal 110. If the potentialtarget home cell 140 does not know its radio frame time offset relativeto the terminal's serving cell 130, it can send an indication to thesource base station 135 requesting an additional cell identifier check.The source base station 135 can request the terminal 110 to determinethe additional cell identifier of the reported home cell 140 and thesource base station 135 can assign a suitable measurement gap to enablethe terminal 110 to read system information of the home cell 140. Theterminal 110 can read system information of the home cell 140 and reportthe additional cell identifier to the serving cell 130. The source basestation 135 at the serving cell 130 can send a message to the potentialtarget base station 145 that sent the indication requesting theadditional cell identifier. The message can include the additional cellidentifier reported by the terminal 110. If the handover request isaccepted, the source base station 135 can send a handover command to theterminal 110. The target base station 145 can then record its radioframe timing offset so that other handovers do not require terminals toread and report the additional cell identifier information.

FIG. 2 is a timing offset illustration 200 according to one embodiment.Radio frame transmissions 240 from a home cell 140 can have a radioframe timing offset 245 relative to radio frame transmissions 230 fromthe serving macro cell 130. Also, radio frame transmissions 250 from ahome cell 150 can have a radio frame timing offset 255 relative to radioframe transmissions 230 from the serving cell 130. The radio frametransmissions 240 from the home cell 140 can also be offset from radioframe transmissions 250 from the home cell 150. The timing offsets 245and 255 can be used to distinguish one home cell 140 from another homecell 150 when the home cells 140 and 150 have the same physical cellidentifier X.

FIG. 3 is an exemplary signal flow diagram 300 according to oneembodiment. The signal flow diagram 300 illustrates signals between theterminal 110, such as user equipment, the serving base station 135, suchas a serving eNodeB, a mobility management entity 310, the home basestation 145, such as a first home base station at a first closedsubscriber group cell with a physical cell identifier X, and a home basestation 155, such as a second home base station at a second closedsubscriber group cell with the same physical cell identifier X. Themobility management entity 310 is not necessary and signals and messagescan be transmitted substantially directly between the serving basestation 135 and home base stations 145 and 155.

In operation, at 315, a cell with the physical cell identifier X becomesa handover candidate. At 320, terminal 110 can send a measurement reportfor a cell with the physical cell identifier X, the measurement reportincluding a radio frame timing offset, to the serving base station 135.At 325, the serving base station 135 can send a handover requestincluding the physical cell identifier and the radio frame timing offsetto the mobility management entity 310. At 330 and 335, the mobilitymanagement entity 310 can forward the handover request to the home basestations 145 and 155. At 340, the home base station 145 can send ahandover request reject message to the mobility management entity 310 ifit does not transmit with the radio frame timing offset from thehandover request. At 345, the home base station 155 can send a handoverrequest accept message to the mobility management entity 310 if ittransmits with the radio frame timing offset from the handover request.At 350, the mobility management entity can forward the handover requestaccept message to the serving base station 135. At 355, the serving basestation 135 can send a handover command to the terminal 110. At 360, theterminal 110 and the target home base station 155 can synchronize andcomplete the handover.

FIG. 4 is an exemplary signal flow diagram 400 according to oneembodiment. The signal flow diagram 400 illustrates signals between theterminal 110, such as user equipment, the serving base station 135, suchas a serving eNodeB, a mobility management entity 310, the home basestation 145, such as a first home base station at a first closedsubscriber group cell with a physical cell identifier X, and a home basestation 155, such as a second home base station at a second closedsubscriber group cell with the same physical cell identifier X. Themobility management entity 310 is not necessary and signals and messagescan be transmitted substantially directly between the serving basestation 135 and home base stations 145 and 155.

In operation, at 415, a cell with the physical cell identifier X becomesa handover candidate. At 420, terminal 110 can send a measurement reportfor a cell with the physical cell identifier X, the measurement reportincluding a radio frame timing offset, to the serving base station 135.At 425, the serving base station 135 can send a handover requestincluding the physical cell identifier and the radio frame timing offsetto the mobility management entity 310. At 430 and 435, the mobilitymanagement entity 310 can forward the handover request to the home basestations 145 and 155. At 440, the home base station 145 can send ahandover request reject message to the mobility management entity 310 ifit does not transmit with the radio frame timing offset from thehandover request. At 445, the home base station 155 can send anadditional cell identifier check request to the mobility managemententity 310 if it does not know its radio frame timing offset. At 450,the mobility management entity 310 can forward the additional cellidentifier check request to the serving base station 135. At 455, theserving base station 135 can send an additional cell identifiermeasurement command and gap assignment to the terminal 110. At 460, theterminal 110 can acquire system information from the home base station155. At 465, the terminal 110 can send an additional cell identifierreport to the serving base station 135. At 470, the serving base station135 can send a message to the mobility management entity 310, which canbe forwarded to the home base station 155 at 475. The message caninclude the additional cell identifier, such as a closed subscribergroup identifier, and can include the radio frame timing offset.

At 480, the home base station 155 can send a handover request acceptmessage to the mobility management entity 310 if it matches theadditional cell identifier from the handover request. At 485, themobility management entity 310 can forward the handover request acceptmessage to the serving base station 135. At 490, the serving basestation 135 can send a handover command to the terminal 110. At 495, theterminal 110 and the target home base station 155 can synchronize andcomplete the handover.

FIG. 5 is an exemplary block diagram of a wireless communication device500, such as the terminal 110, according to a possible embodiment. Thewireless communication device 500 can include a wireless communicationdevice housing 510, a wireless communication device controller 520coupled to the wireless communication device housing 510, audio inputand output circuitry 530 coupled to the wireless communication devicehousing 510, a display 540 coupled to the wireless communication devicehousing 510, a wireless communication device transceiver 550 coupled tothe wireless communication device housing 510 and coupled to thewireless communication device controller 520, an antenna 555 coupled tothe wireless communication device transceiver 550, a user interface 560coupled to the wireless communication device housing 510, and a memory570 coupled to the wireless communication device housing 510. Thewireless communication device 500 can also include a timing offsetdetermination module 590 and a measurement report transmission module595. The timing offset determination module 590 and the measurementreport transmission module 595 can be coupled to the controller 520 byresiding within the controller 520, by residing within the memory 570,by being autonomous modules, and can be software, can be hardware, orcan be in any other format useful for a module on a wirelesscommunication device 500.

The display 540 can be a liquid crystal display (LCD), a light emittingdiode (LED) display, a plasma display, or any other means for displayinginformation. The wireless communication device transceiver 550 caninclude a transmitter and/or a receiver. The audio input and outputcircuitry 530 can include a microphone, a speaker, a transducer, or anyother audio input and output circuitry. The user interface 560 caninclude a keypad, buttons, a touch pad, a joystick, an additionaldisplay, or any other device useful for providing an interface between auser and an electronic device. The memory 570 may include a randomaccess memory, a read only memory, an optical memory, a subscriberidentity module memory, or any other memory that can be coupled to awireless communication device.

In operation, the wireless communication device transceiver 550 can beconfigured to receive a target cell physical cell identifier. Thewireless communication device controller 520 can be configured tocontrol operations of the wireless communication device 500 and can beconfigured to perform other elements of the disclosed methods for awireless communication device. The timing offset determination module590 can be configured to determine a target cell timing offset of aradio frame of the target cell with respect to a reference timing of aserving cell. The timing offset determination module 590 can beconfigured to determine a target cell timing offset by measuring atiming of a radio frame from a target cell base station signal from thetarget cell to determine the timing offset with respect to the referencetiming of a serving cell. The measurement report transmission module 595can be configured to transmit a measurement report including the targetcell physical cell identifier and the target cell timing offset.

FIG. 6 is an exemplary block diagram of a base station 600, such as thebase station 145, according to a possible embodiment. The base station600 can be a third generation partnership project home NodeB having aphysical cell identifier, can be a home cell base station, can be a userbase station, can be a closed subscriber group base station, or can beany other base station that may have a physical cell identifier similarto another base station within a similar coverage area, such as within acoverage area of a macro cell, such as a serving cell. The base station600 can include a base station housing 610, a base station memory 670, abase station controller 620 coupled to the base station housing 610 andcoupled to the base station memory 670, at least one base stationtransceiver 650 coupled to the base station controller 620, an antenna655 coupled to the base station transceiver 650, and a timing offsetcomparison module 690 coupled to the base station controller 620. Thebase station transceiver 650 can be a wireless or a wired transceiverand can include one or more transceivers.

In operation, the base station memory 670 can be configured to store aphysical cell identifier and store timing offset information. The basestation controller 620 can be configured to control operations of thebase station 600. The base station transceiver 650 can be configured toreceive a handover request message including target cell timing offsetinformation. The timing offset comparison module 690 can be configuredto compare the received target cell timing offset information with thestored timing offset information. The base station transceiver 650 canbe configured to send a handover request accept message if the receivedtarget cell timing offset information is substantially equal to thestored timing offset information. The base station transceiver 650 canbe configured to send a handover request reject message if the receivedtarget cell timing offset information is substantially different fromthe stored timing offset information. The base station controller 620can also receive the messages from the base station transceiver 650 andcan prepare the other messages and send them to the base stationtransceiver 650.

The base station controller 620 can be configured to determine timingoffset information of transmitted radio frames of the base station 600with respect to a second base station, such as the base station 135, andcan be configured to store, in the base station memory 670, the timingoffset information of the transmitted radio frames of the base station600. The base station controller 620 can also determine that timingoffset information has not been stored in the base station memory 670.The base station transceiver 650 can then send an additional cellidentifier request message if the timing offset information is notstored in the base station memory 670 and can receive an additional cellidentifier in response to sending the additional cell identifier requestmessage. The base station controller 620 can then determine that thereceived additional cell identifier is equal to an additional cellidentifier of the base station 600 and can store the received targetcell timing offset information in the base station memory 670 if thereceived additional cell identifier is equal to the additional cellidentifier of the base station 600. The base station controller 620 canalso determine the received additional cell identifier is not equal toan additional cell identifier of base station 600. The base stationtransceiver 650 can then send a handover request reject message if thereceived additional cell identifier is not equal to the additional cellidentifier of the base station 600. The additional cell identifier canbe a closed subscriber group cell identifier, a global identifier cellidentifier, and/or any other additional identifier used to identify acell or a base station. The base station controller 620 and the basestation transceiver 650 can also be configured to perform other elementsof the other methods either along with, or independent from theseelements.

FIG. 7 is an exemplary flowchart 700 illustrating the operation of theterminal 110 according to a possible embodiment. At 710, the flowchart700 begins. At 720, a target cell physical cell identifier can bereceived. At 730, a target cell timing offset of a radio frame of thetarget cell can be determined with respect to reference timing of aserving cell. The serving cell can be a macro cell or serving cell thatincludes one or more target cells. The target cell timing offset can bedetermined by measuring a timing of a radio frame from a first targetcell target base station signal to determine the timing offset withrespect to the reference timing of the serving cell. At 740, ameasurement report including the target cell physical cell identifierand the target cell timing offset can be sent. At 750, a handovercommand can be received from a base station of the serving cell toinitiate a handover from the serving cell to the target cell. Thehandover command may or may not include both or one of the target cellphysical cell identifier and the target cell timing offset. At 760, theflowchart 700 can end.

FIG. 8 is an exemplary flowchart 800 illustrating the operation of apotential target cell base station, such as the base station 145,according to a possible embodiment. The potential target cell basestation can be a third generation partnership project home NodeB havinga physical cell identifier or can be any other potential target basestation disclosed in the embodiments. At 810, the flowchart 800 begins.At 820, a handover request message including target cell timing offsetinformation can be received at a potential target cell base station,where the potential target cell base station can have a physical cellidentifier. At 830, the received target cell timing offset informationcan be compared with timing offset information stored at the potentialtarget cell base station. At 840, a handover request accept message canbe sent if the received target cell timing offset information issubstantially equal to the stored timing offset information. At 850, ahandover request reject message can be sent if the received target celltiming offset information is substantially different from the storedtiming offset information. In step 860, the flowchart 800 can end.

FIG. 9 is an exemplary flowchart 900 illustrating the operation of apotential target base station, such as the base station 145, accordingto a possible embodiment. Elements of the flowchart 900 can be combinedwith elements of the flowchart 800. At 910, the flowchart 900 begins. At920, timing offset information of transmitted radio frames of thepotential target cell base station can be ascertained with respect to asecond base station. At 930 the timing offset information of thetransmitted radio frames of the potential target cell base station canbe stored. At 940, the flowchart 900 can end.

FIG. 10 is an exemplary flowchart 1000 illustrating the operation of apotential target cell base station, such as the base station 145,according to a possible embodiment. Elements of the flowchart 1000 canbe combined with elements of the flowchart 800 and/or elements of theflowchart 900. At 1010, the flowchart 1000 begins. At 1020, adetermination can be made as to whether the timing offset information isstored at the potential target cell base station. At 1030, an additionalcell identifier request message can be sent if the timing offsetinformation is not stored at the potential target cell base station. At1040, an additional cell identifier can be received in response tosending the additional cell identifier request message. The additionalcell identifier can be a closed subscriber group cell identifier, aglobal identifier cell identifier, or any other additional identifierused to identify a cell or a base station. At 1050 a determination canbe made as to whether the received additional cell identifier is equalto an additional cell identifier of the potential target cell basestation. At 1060, the received target cell timing offset information canbe stored at the potential target cell base station if the receivedadditional cell identifier is equal to the additional cell identifier ofthe potential target cell base station. At 1070, a handover requestreject message can be sent if the received additional cell identifier isnot equal to the additional cell identifier of the potential target cellbase station. At 1080, the flowchart 1000 can end.

According to some embodiments, home base stations, such as user basestations or closed subscriber group base stations, may not besynchronized to a macro network or to one another. Thus, embodiments canprovide for the frame timing of the home base stations to be used todistinguish between home base stations that use the same physical cellidentifier. When a wireless terminal detects a home base station, it caninclude, in a measurement report, the time offset between transmissionsof radio frames by the serving cell and transmissions of radio frames bythe home base station. The serving cell can attempt to prepare all homebase stations with the reported physical cell identifier by sending ahandover preparation request which can include the reported time offset.The home base station that is transmitting frames with the reported timeoffset with respect to the serving cell can then accept the handoverrequest.

Same frame transmission timing can account for multi-path transmissionsin that a threshold can be defined such that if a wireless terminalreceives two paths corresponding to the same physical cell identifierand the timing difference between the two paths is smaller than thethreshold, then the wireless terminal can regard the two paths asoriginating from the same home base station. This can be done bychoosing a threshold that is larger than a cyclic prefix.

The home base station can have a downlink receiver so that it candetermine its radio frame timing offset with respect to the macro cell,such as a serving cell or a reference cell. Other options can be used toprovide the timing offset to the home base station, such as by havingthe home base station request the timing offset from a wireless terminalvia a serving cell base station. Other options can be considered basedon the reference cell with respect to which the home base station timingoffset is measured. For example, a home base station on a dedicatedcarrier can maintain its radio frame timing offset with respect to oneor more macro cells on another carrier.

Some embodiments can overcome the confusion caused by physical cellidentifier reuse between cells. According to some embodiments a methodin a mobile station in idle state can resolve the physical cellidentifier confusion between cells. The physical layer cell identifierof a first cell can be determined. Then, the radio frame time offset ofthe first cell relative to a reference cell can be determined. Then,whether another cell has the same physical cell identifier as thephysical cell identifier of the first cell can be determined. Then, theradio frame time offset of the another cell with respect to thereference cell can be determined. Then, whether the radio frame timeoffset of the another cell with respect to the reference cell is thesame as the radio frame time offset of the first cell relative to thereference cell can be determined. Then, the presence of the another cellcan be ignored if the radio frame time offset of the another cell withrespect to the reference cell is the same as the radio frame time offsetof the first cell relative to the reference cell.

Some embodiments can provide a method in a mobile station in connectedmode to resolve the confusion of physical cell identifiers betweencells. A potential target base station signal can be measured whileconnected to a serving base station and the radio frame time offset ofthe potential target base station relative to the serving base stationcan be determined. A measurement report can be sent to the serving basestation, where the measurement report can include the radio frame timeoffset of the potential target base station relative to the serving basestation. A handover command can be received from the serving basestation directing the mobile station to handover to the potential targetbase station.

Some embodiments can provide for a method in a network to resolveconfusion of physical layer cell identifiers. A radio frame time offsetwith respect to a second cell can be assigned to a first cell. Radioframes can be transmitted from the first cell such that the radio framesare delayed by a duration equal to the radio frame time offset withrespect to a second cell.

Some embodiments can provide for a method in a base station to resolveconfusion of physical layer cell identifiers. A request to handover amobile station from a first source base station can be received, wherethe request can include at least an identifier of a target base stationfor the handover. A message can be transmitted to the source basestation indicating that a second identifier of the target base stationis required.

The methods of this disclosure are preferably implemented on aprogrammed processor. However, the operations of the embodiments mayalso be implemented on a general purpose or special purpose computer, aprogrammed microprocessor or microcontroller and peripheral integratedcircuit elements, an integrated circuit, a hardware electronic or logiccircuit such as a discrete element circuit, a programmable logic device,or the like. In general, any device on which resides a finite statemachine capable of implementing the operations of the embodiments may beused to implement the processor functions of this disclosure.

While this disclosure has been described with specific embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art. For example,various components of the embodiments may be interchanged, added, orsubstituted in the other embodiments. Also, all of the elements of eachfigure are not necessary for operation of the disclosed embodiments. Forexample, one of ordinary skill in the art of the disclosed embodimentswould be enabled to make and use the teachings of the disclosure bysimply employing the elements of the independent claims. Accordingly,the preferred embodiments of the disclosure as set forth herein areintended to be illustrative, not limiting. Various changes may be madewithout departing from the spirit and scope of the disclosure.

In this document, relational terms such as “first,” “second,” and thelike may be used solely to distinguish one entity or action from anotherentity or action without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. Also,relational terms, such as “top,” “bottom,” “front,” “back,”“horizontal,” “vertical,” and the like may be used solely to distinguisha spatial orientation of elements relative to each other and withoutnecessarily implying a spatial orientation relative to any otherphysical coordinate system. The terms “comprises,” “comprising,” or anyother variation thereof, are intended to cover a non-exclusiveinclusion, such that a process, method, article, or apparatus thatcomprises a list of elements does not include only those elements butmay include other elements not expressly listed or inherent to suchprocess, method, article, or apparatus. An element proceeded by “a,”“an,” or the like does not, without more constraints, preclude theexistence of additional identical elements in the process, method,article, or apparatus that comprises the element. Also, the term“another” is defined as at least a second or more. The terms“including,” “having,” and the like, as used herein, are defined as“comprising.”

We claim:
 1. A method comprising: receiving a handover request messageincluding target cell timing offset information at a potential targetcell base station, the potential target cell base station having aphysical cell identifier; comparing the received target cell timingoffset information with stored timing offset information at thepotential target cell base station; and when the received target celltiming offset information is similar to the stored timing offsetinformation, sending a handover request accept message; and when thereceived target cell timing offset information is not similar to thestored timing offset information, sending a handover request rejectmessage.
 2. The method according to claim 1 further comprising:ascertaining timing offset information of transmitted radio frames ofthe potential target cell base station with respect to a second basestation; and storing the timing offset information of the transmittedradio frames of the potential target cell base station.
 3. The methodaccording to claim 1 further comprising: determining that timing offsetinformation is not stored at the potential target cell base station;sending an additional cell identifier request message if the timingoffset information is not stored at the potential target cell basestation; receiving an additional cell identifier in response to sendingthe additional cell identifier request message; determining that thereceived additional cell identifier is equal to an additional cellidentifier of the potential target cell base station; and storing thereceived target cell timing offset information at the potential targetcell base station if the received additional cell identifier is equal tothe additional cell identifier of the potential target cell basestation.
 4. The method according to claim 3 further comprising:determining the received additional cell identifier is not equal to anadditional cell identifier of the potential target cell base station;and sending a handover request reject message if the received additionalcell identifier is not equal to the additional cell identifier of thepotential target cell base station.
 5. The method according to claim 3wherein the additional cell identifier comprises one of a closedsubscriber group cell identifier and a global identifier cellidentifier.
 6. The method according to claim 1 wherein the potentialtarget cell base station comprises a third generation partnershipproject home NodeB having the physical cell identifier.